Patent Application
20090199537
On diesel engines requiring both NOx and particulate aftertreatment systems, it is likely that some systems will use both urea selective catalytic reducers (SCR) in combination with diesel particulate filters (DPF). In systems where the DPF is located upstream of a urea SCR catalyst, any uncontrolled regenerations or other high temperature excursions in the DPF could also put the SCR at risk of premature aging and failure. In systems where the DPF is upstream of the SCR, this is especially a factor. There is a need to protect the SCR during periods of uncontrolled DPF regeneration to ensure SCR long service life and prevent premature aging and failure caused by exposure to high heat.
In one embodiment, the present invention is directed to a method to operate an electronically controlled internal combustion engine equipped with a Engine Control System (ECS) and an exhaust system with a Diesel Particulate Filter (DPF) having an inlet and an outlet, the DPF located upstream of a Selective Catalytic Reducer (SCR) having an inlet and an outlet and at least one temperature sensor electronically connected to the ECS to transmit data signals to the ECS indicative of the temperature at the SCR inlet. The SCR is in fluid connection with a urea source. The method is directed to protecting the SCR during uncontrolled DPF regeneration. The method comprises the steps of:
determining engine operating mode;
determining whether the DPF is regenerating;
sensing whether the DPF outlet temperature or SCR inlet temperature exceeds a predetermined threshold for a predetermined period of time;
introducing urea to said SCR in an amount sufficient to minimize over-temperature to the SCR during DPF regeneration below said predetermined temperature threshold. In one embodiment, urea is introduced to the SCR by an injector in fluid communication with a urea source. The injector is responsive to commands from said ECS.
The method may further include a clean up catalyst to catalyze any excess ammonia slip that may be produced by the introduction of urea to cool the SCR. The method may further include the use of a dump valve responsive to commands from the ECS to reroute some or all of the exhaust gas in said exhaust system to bypass said SCR during uncontrolled DPF regeneration. The dump valve is controlled by the ESC and actuated responsive to the introduction of urea. If, after the introduction of urea, the SCR inlet temperature continues to exceed a predetermined threshold for a predetermined period of time the ESC actuates the dump valve to divert the flow of exhaust gas from the SCR, thereby cooling the SCR. The diverted exhaust gas may be vented to the atmosphere or diverted around the SCR and from there, out of the exhaust system.
While the method is effective at all modes of engine operation, preferably, enhanced SCR inlet temperature cooling results may be seen when the engine operating mode is engine idle.
In another embodiment, the present invention is directed to a method to operate an electronically controlled internal combustion engine equipped with an Engine Control System (ECS), an exhaust system equipped with a Diesel Particulate Filter (DPF) having an inlet and an outlet. At least one temperature sensor is position proximal to the SCR inlet and is electronically connected to the ECS to transmit data signals indicative of the temperature at the SCR inlet. The DPF is positioned upstream of a Selective Catalytic Reducer having an inlet and an outlet, and the exhaust system is further provided with a protector to prevent overheating of the SCR during uncontrolled DPF regeneration. The method comprises the steps of:
determining engine operating mode:
determining whether the DPF is regenerating;
sensing whether the DPF outlet temperature or SCR inlet temperature exceeds a predetermined threshold for a predetermined period of time;
actuating the protector to prevent overheating of the SCR during uncontrolled DPF regeneration.
In one embodiment, the protector may be comprised of a source of urea and an injector in fluid communication with said urea and said SCR to facilitate the introduction of an amount of urea in sufficient quantity over a sufficient period of time to cool the SCR inlet below a predetermined temperature for a predetermined period of time during uncontrolled DPF regeneration. A clean up catalyst is used to catalyze any excess ammonia slip from the introduction of urea to the SCR during DPF regeneration.
In another embodiment, the protector may be a dump valve actuated by said ECS to divert some or all of the exhaust gas from the SCR during uncontrolled DPF regeneration. The dump valve is responsive to commands from the ECS to divert exhaust from the SCR when the SCR inlet temperature exceeds a predetermined temperature for a predetermined period of time during uncontrolled DPF regeneration.
Whereas the methods of the present invention are useful and operational at all modes of engine operation, enhanced results are seen when the engine is operating at engine idle mode.
Turning now to the drawings wherein like numbers refer to like structures, vehicle system 10 includes internal combustion engine 12 having cylinders 14 disposed within block 16 for reciprocal movement therein. The engine may be of any construction, such as a spark ignition engine or a compression ignition engine, and is preferably a compression ignition type engine. The engine is electronically controlled by an Engine Control System 18 (ECS) that may be comprised of a single module or multiple modules, as is well known in the art. The ECS has memory, such as PROM, EPROM, EEPROM, FLASH, volatile and nonvolatile memory, and may also have tables or maps therein within which are loaded operating instructions and other information necessary for the operation and control of the engine and any system. In a preferred embodiment, the Engine Control System has DDEC operating instructions and programs loaded therein such as is available from Detroit Diesel Corporation. The ECS communicates and controls the engine through the engine communication area network (ECAN) 20 that permits the ECS to receive sensor input from the engine and to send commands from the ECS to control operation of the engine.
The engine has an exhaust system 22 comprised of an exhaust conduit 24 in fluid communication with an exhaust 21 of the engine to vent exhaust gasses 62 out of exhaust exit 60 that are produced in the combustion chambers of the engine to the ambient atmosphere after it is treated for removal of Particulate Matter (PM), and NOx. The exhaust system is preferably equipped with a Diesel Particulate Filter (DPF) 26 to remove PM from the exhaust gasses. The DPF has an inlet 28 and an outlet 30. In close proximity to the DPF outlet, a pressure sensor 32 is disposed to send data signals indicative of DPF inlet pressure to the ECS. The ECS determines if the DPF inlet pressure is indicative of a clogged DPF filter, at which time, it initiates a regeneration of the DPF by controlling fueling, timing, BOT, engine mode of operation, engine load and engine speed, etc., of the engine to create the requisite heat in the exhaust stream to burn the PM and other hydrocarbon contaminates from the DPF filter. Generally, the DPF is upstream from a Selective Catalyst Reducer 42. The SCR has an inlet 44 and an outlet 50. At least one temperature sensor 46 is disposed proximal to said SCR inlet and is in electronic communication 48 with the ECS to transmit data signals to the ECS indicative of the temperature of the exhaust gasses at the SCR inlet. Disposed in conduit 24 intermediate to the DPF and the SCR is a dump or diverter valve 36 that is actuated by the ECS over electronic communication 38 in response to temperature readings received from the temperature sensor 46. Valve 36 may be actuated to divert the flow of exhaust gasses around the SCR when it is determined that the temperature at the SCR inlet exceeds a predetermined threshold for a predetermined period of time. In one embodiment, when the exhaust temperature exceeds that threshold of temperature and time, the ECS actuates the valve to divert the flow of exhaust gas through diverter conduit 40 around the SCR and exits the exhaust gas to the ambient atmosphere through exhaust exit 60. The exhaust system may further be equipped with a urea injector 56 that is electronically controlled by the ECS responsive to the temperature at the SCR inlet. When the temperature inlet temperature exceeds a predetermined threshold for a predetermined period of time, the ECS causes the urea injector to inject urea from urea source 52 through urea conduit 54 to the SCR inlet in an attempt to cool the SCR temperature. The amount of urea to be injected during the methods of the present invention is dependent upon the temperature at the SCR inlet, and is in an amount sufficient to cool the SCR inlet temperature below a predetermined threshold for predetermined period of time. In order to accommodate the injection of urea into the exhaust stream, a catalytic cleaner 64 may be utilized in the exhaust conduit downstream of the SCR to effectively neutralize any ammonia slip caused by the introduction of excessive urea into the SCR during DPF regeneration events.
The words used in the specification are understood to be words of description, and not words of limitation. Many variations and modifications are possible without departing form the scope and spirit of the invention as set forth in the appended claims.
